1. Field of the Invention
The invention relates to a multi-antenna diversity antenna system installed on a conductively framed, dielectric surface in the body of a motor vehicle. This antenna system is for receiving signals in the meter and decimeter wave ranges, for example for radio or television broadcast reception.
2. The Prior Art
Conventional multi-antenna systems are described, for example in European patent EP 0 269 723, and German patents DE 36 18 452; DE 39 14 424, FIG. 14; DE 37 19 692; and P 36 19 704, for windshield and rear window glass panes.
With an adequate high-frequency decoupling of the antennas, reception disturbances occur when the motor vehicle is positioned in different locations in the field of reception. These receiver disturbances occur with temporary level fading events due to the multi-directional propagation of the electromagnetic waves. This effect is explained by way of example in FIGS. 3 and 4 in EP 0 269 723.
When a reception interference occurs in the signal of the antenna of an antenna diversity system that is switched on at a given time, the antenna is reversed to another antenna, and while in a preset field of reception, the number of level fading events leading to reception interference on the receiver input is kept as low as possible. The level fading events, plotted over the driving distance, and thus also over time, do not occur congruently. The probability for finding, among the available antennas, an undisturbed signal, which grows with the number of antenna signals and the decoupling between these signals in terms of diversity.
In the present invention, a decoupling of the antenna signals in a diversity system exists when the reception signals are different, especially when there are reception disturbances such as, when the HF-level faded. To obtain good diversity efficiency, 3 to 4 antenna signals that are adequately decoupled, are required in most practical applications. According to the state of the art, these antenna signals are received on the rear glass window pane of a motor vehicle that is also integrated in the heating field. Therefore, a connection network has to be provided for each antenna. Moreover, an antenna amplifier is also included to provide good signal-to noise ratios. In the great majority of cases, these connection networks are costly, especially in conjunction with the required high-frequency connection lines leading to the receiver.
In the future, modern automobiles will have an increased use of plastic in the auto bodies, for example in the form of plastic trunk lids or plastic components or panels in the otherwise metallic body of the vehicle.
The present invention is an improvement on DE 195 35 250. The antenna structures 5 and 6 are shown in this patent in FIGS. 2 and 4, for different frequency ranges. The antenna structures are shown in the plastic trunk lid, or in the roof cutout of a vehicle. Separate antennas are specified in DE 195 35 250 for each of the various frequency ranges, to obtain the smallest possible couplings by the greatest possible spacing among the antennas of the different frequency ranges. This patent shows a useful special distribution of the antennas within the confined installation space available.
According to the prior art, it would be necessary to additionally employ four connection networks, i.e. antenna amplifiers, for example for receiving UHF radio broadcasts. Their connection to the body of the vehicle in the site of installation, and their wiring, would be connected with considerable expenditure, and would also be very complicated. To design multi-antenna diversity systems with 4 antennas with antenna amplifiers with a ground connection for diversity-UHF-reception, decoupled from each other, a large spacing is needed between each antenna, and 4 separately disposed antennas for the diversity reception of terrestrial television signals need to be provided according to DE 195 35 250. The installation space of this system is consequently not available because of the relatively large wavelengths of the useful frequency ranges.
Therefore, the present invention provides an installation space-saving diversity antenna for a diversity antenna system in a motor vehicle, with received signals that can be selected in different ways. With this design, the average quality of the reception is as good as possible. In addition, the reception disturbances occur simultaneously in the different antenna signals while driving are kept as small as possible.